Current helicopters and other vertical take-off aircraft are extremely complicated and maintenance intensive. As a result, it is often prohibitively expensive to fly helicopters. In practice the use of helicopters is limited to government and commercial operations in which their capabilities are indispensable. Despite their desirable flight characteristics, helicopters are rarely used in general aviation.
Helicopters have captured human imagination since prior to the first successful airplanes. As a result, there have been a variety of proposed helicopter designs. Many of these proposed designs are impractical. Various patents and published patent applications disclose helicopter designs. These include:                U.S. Pat. No. 6,460,482 which discloses a helicopter having two rotors driven coaxially. The rotors can be tilted relative to an airframe of the helicopter.        U.S. Pat. No. 5,791,592 which discloses another tilting coaxial rotor helicopter design.        U.S. Pat. No. 5,370,341 which discloses an ultra lightweight helicopter having coaxial rotors that a pilot can manoeuver by moving his or her center of gravity.        U.S. Pat. No. 5,791,592 which discloses a coaxial rotor helicopter with no tail rotor.        U.S. Pat. No. 6,293,492 which discloses a helicopter having coaxial rotors that can be tilted for directional control.        U.S. Pat. No. 4,912,999 which discloses a helicopter having a transmission and rotors that can be tilted for directional control.        U.S. Pat. No. 2,486,059 which discloses a lightweight helicopter having coaxial rotors.        U.S. Pat. No. 6,182,923 which discloses a helicopter having a rotor and power assembly that is slidable in one direction and pivotal in another.        U.S. patent application publication No. 20020125368 which discloses an ultralight helicopter having tilting rotors.        U.S. Pat. No. 3,722,830 which discloses a helicopter type vehicle having coaxial rotors in which steering is accomplished by shifting a center of gravity of the vehicle.        PCT patent application publication No. WO02/062661A1 which discloses a lightweight helicopter.        
Despite the wide variety of existing helicopters and proposed helicopter designs, there exists a need for practical helicopters which avoid at least some disadvantages of the prior art. There is a particular need for practical helicopters which are suitable for general aviation use and for practical helicopters having sizes intermediate proposed one-person personal helicopters and larger commercial helicopters.